An American doctor who contracted Ebola while volunteering in Liberia has selflessly given the only dose of life saving serum to a colleague also infected with the deadly virus.

Dr. Kent Brantly, 33, heroically requested the last dose of the drug be given to fellow worker Nancy Writebol, 60, after only a small amount of the medicine arrived in the disease plagued part of Liberia where the pair had been working, according to the Samaritan’s Purse charity.

“Yesterday, an experimental serum arrived in the country, but there was only enough for one person,” said Samaritan Purse President Frank Graham. “Dr. Brantly asked that it be given to Nancy Writebol.”

Both Brantly and Writebol had initially showed signs of improvement after being diagnosed with Ebola, but their health took a turn for the worse Thursday, causing doctors to downgrade their conditions to grave.

The two Christian missionaries had been volunteering at an Ebola relief center in Liberia’s capital city of Monrovia when they somehow both became infected.

Brantly, who had been treating sick patients, immediately isolated himself after showing symptoms which can include fever, headaches, vomiting and rash.

Writebol, who worked as a hospital hygienist, fell ill soon after.

Brantly’s family had been living with him in Liberia but returned to the United States just days before he became infected.

“As people with a deep faith in Jesus, we sincerely thank the thousands of people worldwide who have lifted up Kent and this dreadful situation in prayer,” the brave doctor’s family said in a statement.

“We continue to lean on that faith and take great consolation in our God in these times.”

Samaritan’s Purse said it is currently in the process of evacuating all non-essential personnel to their home and hoped to be finished by this weekend.

More than 600 people have died since the Ebola outbreak began sweeping through the west Africa.

The United States has urged travelers not to visit Liberia, Sierra Leona or Guinea.